In the interests of full disclosure, I should point out that I actually don't have any babies, so I can't say definitively if this fits, but I use this very helpful website as a guide.
The finished hat shown below measured 12" in circumference and was 7 " long, allowing the rim to be turned up. Because I turned every row, there is no 'wrong' side to the rim. It came out good and stretchy too, so should fit bub for a little while.
Ripple Baby Beanie
Yarn: Bendigo Woollen Mills Luxury 4ply baby wool (though any 4 ply should do)
I use UK terms, but have inluded US terms in parenthesis.
Additionally, I have included instructions on how to give this hat the ridged effect to match the cardigan in the set. If you don't want the ridged effect, don't turn your work, but continue in a spiral. This will mean that your finished hat will not be reverseable, and your rim will show the wrong side of the crochet.
I do not turn the work until row 5, but you could turn before if desired.
To start: ch 4 and join to form a loop.
Round 1: ch 3 (counts as tr(dc) here and throughout), 13 tr(dc) into loop, join with sl st [14 st].
Round 2: ch 3, *sk 1 st, 5 tr(dc) in next st**, repeat from * to **, 4 tr(dc) into same st as starting ch 3, join with sl st.
Round 3: sl st across one st, ch 3, *tr(dc), tr(dc) 5 into next st, tr(dc), sk 2 st**, repeat from * to **, sl st into 3rd ch of beginning ch 3 to join.
Round 4: sl st across one st, ch 3, *2 tr(dc), tr(dc) 5 into next st, 2 tr(dc), sk 2 st**, repeat from * to **, sl st into 3rd ch of beginning ch 3 to join.
Round 5: turn, sl st across two sts, sl st across to next st in blo, ch 3, *3 tr(dc) blo, tr(dc) 5 into next st, 3 tr(dc) blo, sk 2 st**, repeat from * to **, sl st into 3rd ch of beginning ch 3 to join.
Can you see the pattern? Essentially you want 5 tr(dc) in the middle tr of the 5 tr(dc) of the row below, tr(dc) in all other sts and always skipping two st on top of the 2 sts skipped in the previous row. You could make this hat to fit any head by continuing this way to your desired size.
Round 6: turn, sl st across two sts, sl st across to next st in blo, ch 3, *4 tr(dc) blo, tr(dc)
Round 7-19: repeat round 6.
End off, weave in ends.
Please let me know if you have any issues with the pattern, and I would love to see your FOs should you make your own!
Link up your projects with the pattern on ravelry here!!
**Update 4/9/12: correction made to pattern (see red text above)